The term "biomass" generally describes a collection or mass of organic material or residue of organic material. Sources of biomass include wood chips or sawdust, straw, sugar cane bagasse, corn stalks, barley husks and other harvesting and agricultural residues.
Xylose-rich oligosaccharide, also termed xylans or pentosans became of their prevalent pentose content, can be isolated from various biomass resources by extraction with water and aqueous alkali. The release of xylans from biomass may be assisted by any one of many optional pre-treatment procedures, such as steam explosion, organosolv pulping, mild hydrolysis, etc. Many procedures for isolating xylans from biomass have been described, including the technique described in our co-pending patent application referenced above. Xylose-rich oligosaccharides and polysaccharides are also generally available commercially from such sources as Sigma Chemical Company, St. Louis, Mo.
Xylan serves structural biomass components, such as wood, straw, fruit hulls, and nuts, etc., as a biodegradable interfacial compatibilizer which assists in the stress transfer of the reinforcing cellulose fibers to the continuous lignin-rich matrix. Xylans are the constituents of biomass that degrade most rapidly when biomass rots in the natural environment. It is generally believed that xylan is capable of performing these functions by combining the chemical structural features of cellulose (the reinforcing fiber component) with the morphological structural features of lignin (the continuous amorphous network). At the same time xylan retains the biodegradability characteristics of such non-crystalline polysaccharides as starch, and it is biodegradable and/or environmentally degradable even after extensive chemical modification, such as by branching and acetylation, has taken place.
Several xylan derivatives have been described and may be generally known to those of ordinary skill in the art. The term "xylan derivative" refers to a xylan that has been modified to alter its chemical or molecular structure. None of the heretofore described xylan derivatives have been produced utilizing a procedure that allows the thermal responses of the xylan derivative, such as glass to rubber transition and melting point, to be selectively tailored in relation to the type and extent of modification. This is the subject of the current disclosure.
Whereas "thermoplastic" derivatives of cellulose and starch are known, similar thermoplastic derivatives have not been described for xylan. The term "thermoplastic" as utilized herein refers to a high polymer that softens when exposed to heat, and becomes deformable in this condition, and returns to its original condition when cooled to room temperature. Thus, "thermoplastic xylan derivatives" are xylan derivatives which exhibit this behavior.
It is generally known that xylans have significantly different solubility characteristics than cellulose or starch, and different chemical and molecular structures than cellulose or starch. Due to xylans' significantly different solubility characteristics, i.e., solubility in aqueous alkali but insolubility in virtually all organic solvents; and due to xylans' different chemical and molecular structure, i.e., branched, amorphous, composed of several different types of monosaccharides (heteropolysaccharides), and consisting of different types of functional groups (i.e., OH groups, acetoxy groups, carboxy groups, methyl ether groups, etc.) xylans represent a different type of polysaccharide that behaves differently during modification than cellulose and/or starch derivatives.
It would be advantageous to produce xylan derivatives with known properties in relation to important thermal responses such as softening and melting.
It would also be advantageous to produce a melt flowable biodegradable and/or environmentally degradable xylan derivative with the ability to interact with other natural and melt flowable materials on account of being chemically and molecularly compatible with other polymeric components.
It would be further advantageous to be able to isolate thermoplastic xylan derivatives in substantially pure form from the mixtures of components found in aqueous extracts of biomass or aqueous solutions of oligosaccharides and polysaccharides.